Using the solid waste-quicklime membrane swqm process for the production of sodium hydroxide

ABSTRACT

The proposed invention uses ion exchange technology to produce dilute caustic soda liquor from calcium hydroxide liquor Ca(OH) 2  followed by the reaction of carbon dioxide CO 2  with caustic soda to produce dilute sodium carbonate solution. Multiple reverse osmosis and acidic CO 2  sparging can concentrate the Na 2 CO 3  liquor to 6-7%. The 6-7% liquor is treated with waste heat to produce 50% or solid Na2CO3. The 6-7% liquor can be treated with Ca(OH) 2  to produce 6-7% NaOH liquor then can be transformed to 50% or solid NaOH. The output of many industrial processes generates waste heat, brine water and CO2 and the present invention combines these components in the production of solid Na 2 CO3, NaOH or their high % liquors. Availability of waste heat sources can lead to higher efficiency in Na 2 CO 3  and NaOH production. The process is not electrochemical chloro alkali technology or Solvay process.

TECHNICAL FIELD AND BACKGROUND INFORMATION

Using heat generated from solid waste incineration (or any available source of waste heat) with brine water, acidic water, and advanced membrane and resin technology in the production of soda ash Na2CO3 and sodium hydroxide NaOH.

From a pre-limer calcium hydroxide Ca(OH)2 (500 to 1000 ppm) is processed by a cation exchange system (strong or weak) to produce sodium hydroxide (500 to 1000 ppm) such that:

Ca(OH)2+2R-Na⁺→2NaOH+R-Ca++

The present invention uses a classical equation where CO2 is reacted with caustic soda NaOH to produce clear solution of sodium carbonate Na2CO3 such that:

NaOH+CO2→Na2CO3

Presence of regenerants such as brine water with a salinity of 6 to 12%, acidic water with acidity of >8% (e.g. HCl or H2SO4) or a combination of both is crucial because it is used to regenerate the cation exchanger such that:

(1) R-Ca+++2NaCl→2R-Na++CaCl2

(2) R-Ca+++HX→2R-H+CaX

-   -   R-H+NaCl→R-Na++HCl (acidic waste)

One aspect of the present patent requires a sparging reactor to bubble acidic flue gas where gases such as HCl and SO2 can be captured to produce acidic solutions such that,

HCl(g)+H2O→HCl(aq) used for strong ion exchange regeneration

SO2(g)+H2O+O→H2SO4(aq) used for strong ion exchange regeneration

Acidic waste can be combined with basic waste such as power plant ash to produce neutral output that can be discharged safely to environment.

Sodium carbonate liquor produced is of low percentage ie 0.05 to 0.5% and need to be concentrated to ˜6%. The concentration process is performed using reverse osmosis system where the Na2CO3 liquor is taken through multiple passes until the final concentrate output is around 6%. Industrially a concentration of 6% is low to extract the solid economically a major setback for membrane technology. The difficulty in going above 6% with existing membrane technology is the high pressure that deteriorates the membrane. Even if recompression evaporation is used around 1 MW is required to produce one ton of solid product. In the present invention the most obvious heat source is the heat emitted by solid waste incineration or any other waste heal source.

Description of how the invention addresses a technical problem

Solid waste, brine water waste, and CO2 waste are major problems faced by human communities worldwide. The proposed invention attempts to bring these three waste problems in one industrial process to bring about a green solution while making a financial benefit. The green solution is fulfilled by large elimination of the various wastes stated above. The financial benefit comes from selling the soda commodity chemicals as byproduct of the combined processes. In a sense the production of NaOH by the WHQM process is an alternative to the chloro-alkali cell process that is used worldwide to produce caustic soda NaOH. Major problem in the chloro-alkali cell process it is tied up to chlorine production and chlorine is a poisonous gas that must find a safe storage. Production of caustic soda using WHQM process is chlorine independent. The process essentially relies on advanced membrane technology systems to produce sodium hydroxide NaOH. Therefore, it is very different from chloro-alkali process that works on high consumption of electrical power (i.e. 3000 KWH per ton of NaOH) to convert NaCl to NaOH. In the present invention the only byproduct is CaCO3 while in chloro-alkali technology dangerous gases such as chlorine and hydrogen have to be handled safely.

DETAILED DESCRIPTION OF THE INVENTION AND DESCRIPTION OF DRAWINGS

Heat from solid waste incinerators (or any other waste heat source) can be utilized as discussed in patent # PCT/1B2008/002020. The mechanism of NaOH production follows a similar scheme as the NaHCO3 production as shown in FIG. 1 on page 9:

Sparger design: Acidic flue gas can be sparged under pressure to dissolve the acidic gas in sea water or river water to form acidic liquor that can be used in strong or weak ion exchange regeneration. Ion exchange system: Would receive the calcium hydroxide liquor Ca(OH)2 (e.g. ˜0.5-1 g/L) to produce a dilute caustic soda liquor at 1000 ppm concentration. Reactors design: Carbon dioxide gas is sparged through caustic soda NaOH in a reactor to form a dilute sodium carbonate liquor Na2CO3 (e.g. 700 ppm Na2CO3 to 300 ppm NaOH). The latter is then subjected to further filtration to remove impurity particulates then passed to reverse osmosis system. The low % liquor needs to be converted and concentrated to higher % sodium carbonate Na2CO3 liquor (e.g. 2400 ppm Na2CO3 to 1000 ppm NaOH) by passing it to a reverse osmosis system.

Reverse osmosis (RO) unit contains RO cartridges cascaded with the CO2-NaOH reactors in between. The objective is to keep the NaOH concentration below 300 ppm as the concentration of Na2CO3 is increased. That is, keep the pH˜11.

Kindly refer to FIGS. 3A, 3B and 3C showing mass balance analysis of the entire process (Pages 11,12,13).

Flow chart of the ion exchange reverse osmosis system:

Flow chart of the ion exchange reverse osmosis system (Kindly refer to FIG. 2 on page 10) Keep going until a 6% Na2CO3 solution (not soda ash powder) is obtained. At this point Na2CO3 solution (i.e. 6%) if evaporated by the available waste heat would produce dry soda ash. However, when 3.5% Na2CO3 is treated with Ca(OH)2 solution, we get:

Na2CO3+Ca(OH)2→2NaOH+CaCO3↓

It is indicated in the worksheet that 24 kg of Ca(OH)2 and ˜20 kg of NaCl are consumed to generate 13 kg of NaOH and 16 kg of CaCO3. In terms of effective evaporation, 1 MWH of thermal energy is required to produce one ton of dry NaOH. If the thermal energy is available as waste heat then we don't need to pay the 1 MWH penalty.

From the WHQM process patent # PCT/1B2008/002020, waste heat that is provided by the solid waste processing unit can convert water into steam of 120 to 150° C. having a boiler above the solid waste incinerator. The steam can be used to convert the 7% sodium hydroxide liquor to 50% liquor by evaporating half the volume or until it is dry sodium hydroxide. Ion exchangers that are used in this process are regenerated from either processed seawater or produced brine water. In the above schematic, if brine water concentration C is >10% salinity then the complex membrane and heat exchanger system is not needed. If brine water concentration 6%<C<9% salinity then the complex membrane is not needed and the heat exchanger system can be used to raise its concentration to 10% or if it is cheaper NaCl is added to bring Cup to 10%. If only seawater is available and the flue gas contains acidic gases such as hydrogen chloride and sulfur dioxide then these gases can be sparged with seawater under pressure to produce acidic sea water suitable for ion exchange processes. The acidic seawater can be used as a regenerent to eliminate the calcium and magnesium ions while sea water is used to wash the regenerated ion exchange and convert it to the Na+ form.

One important aspect about this process is the circulation of RO permeate which save on pure water production and chemicals supply. There are waste products such as calcium chloride and magnesium chloride that can be diluted with the pure water produced from the complex membrane and heat exchanger system and returned back to the sea without harming the marine environment. The net production of potable water is difficult to estimate at this stage and depends on the government tolerance level of Ca++, Mg++ salts after dilution.

Examples of intended use and other methods of industrial use

The WHQM process is most convenient for industries that emit brine water (i.e. salinity between 6 to 16%) and lack any waste heat and CO2 sources. However, it can also work on industries that emit a limited amount of CO2 where the combined amounts from an industrial plant and the solid waste plant can be harnessed in CO2 sequestration and caustic soda production. A solid waste process can operate on a large scale where solid waste incineration can be harnessed to generate CO2, brine water, and heat for the WHQM process. The process can also accommodate flue gas emissions that contain acidic gases that can be harnessed in ion exchange regeneration.

Several advantages gained include CO2 and acidic gases (i.e. HCl & SO2) sequestration. The former is known to cause global warming while the latter causes acid rain in far away regions. 

1. The process by which ion exchange technology to produce dilute caustic soda liquor from calcium hydroxide liquor Ca(OH)2 followed by the reaction of carbon dioxide CO₂ with caustic soda to produce dilute sodium carbonate solution. Multiple reverse osmosis and acidic CO2 sparging can concentrate the Na2CO3 liquor to 6-7%. The 6-7% liquor is treated with waste heat to produce 50% or solid Na2CO3. The 6-7% liquor can be treated with Ca(OH)₂ to produce 6-7% NaOH liquor then can be transformed to 50% or solid NaOH. The invention requires three chemicals CO₂, Ca(OH)₂, and sodium chloride NaCl to produce NaOH. The output of many industrial processes generates waste heat, brine water, and CO₂ and the present invention combines these components in the production of solid Na2CO3, NaOH or their high % liquors. Availability of waste heat sources can lead to higher efficiency in Na2CO3 and NaOH production. The process is not electrochemical chloro-alkali technology or Solvay process. There are similarities in the hardware in patent # PCT/1B2008/002020 but the present patent differs in the mechanism of operation of the ion exchange reverse osmosis system and includes utilization of acidic flue gas.
 2. The present invention uses the SWQM process in patent# PCT/1B2008/002020 to eliminate the need for high consumption of electric power as in chloro-alkali technology.
 3. The use of brine and acidic water and advanced membrane and resin technology in solid waste processing and the production of soda ash Na2CO3 and caustic soda NaOH.
 4. The process by which this invention attempts to bring solid waste, brine water waste, acidic water waste extracted from acidic flue gas, and CO2 waste problems in one industrial process to bring about a green solution through large elimination of the various wastes stated above while making a financial benefit from selling the soda or caustic soda commodity chemical as byproduct of the combined processes.
 5. The process which essentially relies on advanced membrane technology systems to produce soda ash Na2CO3 and caustic soda NaOH we claim the following combined stages (i) to (iv) of the process: (i)- Sparger design: Acidic flue gas can be sparged under pressure to dissolve the acidic gas in sea water or river water to form acidic liquor that can be used in strong or weak ion exchange regeneration. (ii)-Ion exchange system: Would receive the calcium hydroxide liquor Ca(OH)2 (e.g. ˜0.5 g/L) to produce a dilute caustic soda liquor at 1000 ppm concentration or higher depending on the type of ion-exchanger used. (iii)-Reactors design: Carbon dioxide gas is sparged through caustic soda NaOH in a reactor to form a dilute sodium carbonate liquor Na2CO3 (e.g. 700 ppm Na2CO3 to 300 ppm NaOH). The latter is then subjected to further filtration to remove impurity particulates then passed to reverse osmosis system. The low % liquor needs to be converted and concentrated to higher % sodium carbonate Na2CO3 liquor (e.g. 2400 ppm Na2CO3 to 1000 ppm NaOH) by passing it to a reverse osmosis system under controlled pH conditions. (iv)-Reverse osmosis (RO) unit contains RO cartridges cascaded with the CO2-NaOH reactors in between. The objective is to keep the NaOH concentration below 300 ppm as the concentration of Na2CO3 is increased. 